fix: add splitscreen, fix dlcs not loading, major RCE vuln fix on packet net, fix chunk loading on non-server clients, persistent saves

note: I changed how XUID works, player data might be wiped on old saves, save items on a chest or similar before trying to load old saves on new version

Minecraft.World/ByteArrayOutputStream.cpp

@@ -51,14 +51,23 @@ void ByteArrayOutputStream::write(byteArray b)
 //len - the number of bytes to write.
 void ByteArrayOutputStream::write(byteArray b, unsigned int offset, unsigned int length)
 {
-	assert( b.length >= offset + length );
+
+	if (offset > b.length || length > b.length - offset)
+		return;
+
+	if (length > 0xFFFFFFFF - count)
+		return;
 
 	// If we will fill the buffer we need to make it bigger
 	if( count + length >=  buf.length )
-		buf.resize( max( count + length + 1, buf.length * 2 ) );
+	{
+		unsigned int newSize = (std::max)( count + length + 1, buf.length * 2 );
+		if( newSize <= buf.length )
+			return;
+		buf.resize( newSize );
+	}
 
 	XMemCpy( &buf[count], &b[offset], length );
-	//std::copy( b->data+offset, b->data+offset+length, buf->data + count ); // Or this instead?
 
 	count += length;
 }